The overall objectives of the project are: 1) to determine whether changing from one gait to another is a mechanism for minimizing energy expenditure and maximizing muscular efficiency as animals increase speed; and 2) to determine the relationship between muscular activity and basal metabolism by studying the effect of equalizing daily activity of species with widely divergent basal metabolic rates. During the past year, we have measured the electrical activity of 14 locomotory muscles of dogs as they increase speed within each gait and as they change from one gait to another. In the coming year we propose to extend these to a second quadruped. We have also completed studies to determine the population of active fibers as a function of speed and gait (using glycogen depletion in individual fibers) on lions and white rats. We are continuing these studies. We are using rats, desert hedgehogs and varanid lizards to investigate the relationship between muscular activity and basal metabolism.